The present invention relates to a transparent layered product including a glass sheet and a coating film with a rough surface and to a glass article using the same (for example, a photoelectric conversion device, a multiple-glazing unit, or the like).
A transparent layered product in which a thin film such as a tin oxide film or the like is formed on a glass sheet has been used widely for a thin film photoelectric conversion device (a thin film solar cell) or the like. It has been known that tin oxide in a film formed on a glass sheet by a pyrolytic process becomes a polycrystalline product. The polycrystalline product of tin oxide has a surface with roughness caused by the growth of crystal grains according to the increase in film thickness. In a thin film photoelectric conversion device, the surface roughness of a tin oxide film as a transparent electrode enables conversion efficiency to be improved by a light trapping effect. Therefore, various aspects of the shape of the surface roughness of a tin oxide film have been studied.
For example, JP 61-288473 A discloses a thin film photoelectric conversion device including a tin oxide film having a rough surface including convex portions with heights in the range between 100 and 500 nm and intervals between respective convex portions in the range between 200 and 1000 nm. The rough surface is formed by etching after film formation.
Further, JP 2-503615 A discloses a substrate for a thin film photoelectric conversion device including a tin oxide film having a surface provided with convex portions having diameters in the range between 0.1 and 0.3 xcexcm and a ratio of height/diameter in the range between 0.7 and 1.2. In addition, JP 2-503615 A also discloses a chemical vapor deposition method (a CVD method) using a mixed gas containing tin tetrachloride, water vapor, methyl alcohol, nitrogen and the like, which is carried out on a precut glass sheet, as a method of manufacturing a tin oxide film.
JP 4-133360 A discloses a thin film photoelectric conversion device including a tin oxide film having a surface with pyramidal convex portions with heights in the range between 100 and 300 nm and angles with respect to the normal line of the principal plane of its substrate in the range between 30xc2x0 and 60xc2x0. Similarly, JP 4-133360 A also discloses a CVD method using a mixed gas containing tin tetrachloride, oxygen, nitrogen and the like, which is carried out on a glass sheet with a temperature in the range between 350xc2x0 C. and 500xc2x0 C., as a method of manufacturing a tin oxide film.
Besides the tin oxide film, coating films formed of zinc oxide, ITO (indium tin oxide), titanium oxide, or the like also are formed on a glass sheet to add various functions. The coating films also have surfaces with roughness caused by the growth of crystal grains, although the roughness varies depending on the manufacturing method or the like. These coating films are formed on a glass sheet as, for example, a reflection-suppression film, an electromagnetic shielding film, an antifouling film, a low-emissivity film (Low-E film), or as a component of such films, in addition to a transparent conductive film.
Judging from the fact that a porous surface has a refractive index distribution in the depth direction, it is conceivable that a transition layer with a refractive index distribution is present at the surface of a coating film having a rough surface. The thickness of the transition layer can affect the light transmittance of a transparent layered product. Conventionally, however, attention merely has been paid to the physical shape and size of convex or concave portions of the rough surface particularly in a tin oxide film. The thickness of the transition layer produced at the surface of the coating film does not depend only on the shape and size of the individual convex or concave portions of the rough surface but also is affected by the distributions of the shape and size of them. Therefore, the transition layer should not be evaluated based on the observation of the rough surface in a very limited region by an electron microscope and is required to be evaluated based on optical measurement.
It is an object of the present invention that in a transparent layered product including a glass sheet and a coating film exhibiting various functions, the light transmittance of the transparent layered product is increased by suitably controlling the thickness of a transition layer at the surface of the coating film. Further, another object of the present invention is to provide a glass article using this transparent layered product, particularly a photoelectric conversion device such as a photovoltaic device.
The present inventors found that the aforementioned objects were able to be achieved by setting the ratio in the thickness of the transition layer in the coating film to be a predetermined ratio. The transparent layered product of the present invention includes a glass sheet and a coating film having a surface with roughness, which is formed on the glass sheet, and a transition layer in which the refractive index varies continuously in its thickness direction is present at the surface of the coating film. The transition layer has a thickness in a range between 13% and 65% of the thickness of a layer having a substantially constant refractive index in the coating film.
When the coating film is formed as an outermost layer, the refractive index in the transition layer varies continuously in its thickness direction to approach the refractive index of air (1) from the refractive index of the coating film, in the direction of the outside air. On the other hand, when another thin film is further formed on the coating film, the refractive index in the transition layer approaches the refractive index of the another thin film while varying continuously in its thickness direction.
In the transparent layered product, it is preferable that the coating film is a crystalline coating film. It also is preferable that the roughness is caused by crystal grains in the crystalline coating film. In this connection, the crystalline coating film may contain amorphous portions regionally, and a film with a crystalline fraction in volume of at least 50% as a whole is taken as corresponding to a xe2x80x9ccrystallinexe2x80x9d film.
In the transparent layered product, it is preferable that the crystalline coating film contains, as a main component, at least one selected from tin oxide, zinc oxide, indium oxide, and titanium oxide. Particularly, a coating film containing tin oxide as the main component is useful for many purposes. In this specification, the xe2x80x9cmain componentxe2x80x9d denotes a component accounting for at least 50 wt. % of the Whole amount.
In the transparent layered product, it is preferable that the coating film is formed on an undercoating film on the glass sheet. The formation of the undercoating film serves as a means for adjusting the ratio of the transition layer. In this case, it is further preferable that the undercoating film is a coating film formed by pyrolysis of a material containing halogen, and the undercoating film has a surface with roughness caused by production of or loss after the production of compound grains of an alkaline component in the glass sheet and the halogen.
In the transparent layered product, it is preferable that the thickness of the coating film is in a range between 400 nm and 1200 nm. The thickness also is one of the factors affecting the ratio of the transition layer. Particularly, when the roughness is caused by the crystal grains, generally the roughness at the surface tends to increase as the crystal grains grow.
In the transparent layered product, the coating film may be an insulating coating film, but preferably is a conductive coating film (a transparent conductive film).
The transparent layered product can be used for various purposes. For example, it can be used as reflection-suppression (anti-reflection) glass, electromagnetic shielding glass, glass to be electrified for preventing fogging (defogging glass), antifouling glass, antistatic glass, low-emissivity glass (Low-E glass), glass for information display equipment, or glass for a top plate of a duplicator.
The transparent layered product may be used as a glass article by being combined with other members. For example, the present invention includes a multiple-glazing unit in which at least two transparent substrates are positioned to face each other via at least one inner layer selected from a group consisting of an air layer, an inert gas layer, and a low pressure layer and at least one of the transparent substrates is the transparent layered product.
The transparent layered product also can be used as a substrate for a photoelectric conversion device. The photoelectric conversion device includes: a transparent layered product having a glass sheet and a conductive crystalline coating film, which is formed on the glass sheet; at least one photoelectric conversion unit; and a back electrode. The crystalline coating film includes, on its surface, a transition layer in which the refractive index varies continuously in its thickness direction. The photoelectric conversion unit and the back electrode are stacked on the crystalline coating film in this order. The transition layer has a thickness in a range between 13% and 65% of the thickness of a layer having a substantially constant refractive index in the crystalline coating film.